1. Field of the Invention
This invention relates to an image capturing apparatus having a mechanism for adjusting the focus of the optical system thereof according to the video signal from an image sensor.
2. Description of the Related Art
Many digital single-lens reflex cameras have recently been and are currently provided with an electronic viewfinder function (also referred to as a live view function). With the electronic viewfinder function, an image of the subject being shot by the camera is displayed on the display panel arranged on the rear side of the camera. In other words, the display panel operates as a viewfinder.
Since cameras having such an electronic viewfinder function can display an image of the subject being shot by the camera on the display panel, the user can make sure if the subject is there and the framing is good or not without looking at the viewfinder. Therefore, if the user wants to take an unusual shooting position such as a very elevated position or a low position close to the ground, he or she is not required to adopt a difficult posture for the camera shooting. Additionally, since the subject is displayed as an electronic image on the camera, the user can check if there is any problem such as blackout and/or whiteout in the image.
Generally, many single-lens reflex cameras can be operated in either of two focus modes including a manual focus mode where the user manually adjusts the focus and an autofocus mode where the focusing sensor mounted inside the camera detects the out-of-focus condition, if any, and automatically adjusts the focus.
Normally, the user of a single-lens reflex camera having an electronic viewfinder function more often than not selects a manual focus mode because he or she can not utilize the focusing sensor as long as the electronic viewfinder function is in operation. However, it is difficult for the user to find out a delicate out-of-focus condition, seeing the live view on the display panel. On the other hand, an image acquired by a digital camera can be enlarged and displayed with ease afterward to find out any problem in the image. Then, the user of a digital camera may be dissatisfied when he or she detects a delicate out-of-focus condition in the image after shooting.
In view of such a problem, techniques have been proposed for enlarging a part of the image on the viewfinder that the user wants to bring into a manual focus. However, such a technique is accompanied by problems including that delicate focusing is crucial and that the entire image on the viewfinder cannot be viewed at the same time. Amateur photographers may find such problems very bothersome. Even skilled photographers may not be able to successfully deal with such problems when taking handheld shots.
Jpn. Pat. Appln. Publication No. 2007-108217 proposes a digital camera having a feature of assisting the user of a camera in a manual focus mode. A digital camera proposed in Jpn. Pat. Appln. Publication No. 2007-108217 is provided with a manual focus feature of moving the focus lens according to the rotated position of a focusing ring and a focusing feature of automatically setting the focus lens at the position where the best in-focus condition can be achieved and adapted to adjust the focus so as to put the subject selected by the user not remarkably out of focus by making it possible to define the movable range of the focusing lens stepwise when adjusting the focus.